DESCRIPTION (Applicant's Abstract): This research proposal examines the hypothesis that limitations on our attentional abilities can be modified by dynamic interactions between brain regions. Typically, researchers examining the neural bases of attention determine the manner in which specific brain regions perform certain attentional functions. For example, posterior parietal regions have been implicated in disengaging attention from a particular point in visual space. Although most researchers examining the neural basis of attention conceive of it as a network of structures working in concert, the manner in which the interplay of these various brain structures modulates performance remains unspecified. The research in this proposal will address this important shortcoming by proposing that it is the dynamics between brain regions, rather than the specific processing performed by brain regions, that influences certain aspects of attentional functioning. In particular, the proposal will examine the hypothesis that dynamic interactions between the cerebral hemispheres have profound effects on attentional functioning because these dynamics modulate the capacity of the system. Dividing processing across the hemispheres is proposed to be useful when processing load is high or when competing information is present because information is dispersed across a large expanse of neural space. In contrast, this dispersal of processing is detrimental when the processing load is light or when complementary information must be processed. Three series of experiments are designed to systematically evaluate this hypothesis. The first series of experiments tests whether division of processing across the hemispheres will increase processing capacity when attention must be paid selectively to certain attributes of a stimulus while other attributes are ignored. The second series of experiments tests whether a division of processing across the hemispheres reduces both interference and facilitation in two common attentional paradigms: the Stroop paradigm and the Navon global/local paradigm. The third series of experiments tests whether the ability to simultaneously perform two tasks increases when one of the two tasks requires continuous interaction between the hemispheres as compared to when neither do. The outcome of these studies will not only expand our understanding of the neurocognitive bases of attention but will also provide the foundation for future studies that can test the hypothesis that attentional deficits in certain clinical populations with callosal dysfunction, such as schizophrenics, are linked to impairments in hemispheric dynamics.